- 27th November 2020 -

Tree Diseases: UK Threats

Tree Diseases UK Threats

Having laid waste to billions of trees across the UK, tree diseases and pests are a serious threat to the economy and the environment. Here are 5 common diseases and their symptoms.

Is the crown of your oak tree thinning rapidly or have you noticed strange orange growths on your sweet chestnuts? Are your elm trees dying from the top down or have you spotted diamond-shaped dark spots on your ashes?

We look at 5 of the tree diseases UK landowners have been most plagued by over the past few decades. We point out the symptoms to look out for and what you should do if you suspect a pest or disease.

Ash dieback tree disease

Ash dieback disease (Hymenoscyphus fraxineus), also known as chalara, is a fungal tree disease found throughout the UK. Originally from Asia, ash dieback disease is thought to have been accidentally imported from Europe over 30 years ago. The fungus is expected to decimate the UK’s population of common ash trees causing severe ecological and economical damage. It can kill young trees very quickly but older trees can often survive for many years before eventually dying.

Another risk on the horizon comes from the emerald ash borer. This slim, green beetle lays clusters of eggs in ash bark crevices. It has yet to arrive in the UK but has killed billions of trees in the United States. It is thought to be only a matter of time before the beetles do find their way to the UK and attack our already threatened common ash populations.

Symptoms of ash dieback disease include:

  • Leaves that develop dark patches before turning black and wilting
  • Diamond shaped patches of damage where branches meet the trunk. These are brown-grey in colour.
  • Dieback of shoots and leaves in the summer
  • ‘Epicoral’ growth where dormant shoots low down on the trunk start to sprout. This is a common response to stress in trees.

If you suspect ash dieback disease is affecting trees you are responsible for, you should contact an experienced tree surgeon like Arborcure urgently. Felling of all trees may not be necessary but we can provide a professional inspection and help you to minimise the damage and risk of spread.

Dutch elm tree disease

You will probably have heard of the notorious Dutch elm disease (Ophiostoma novo-ulmi). Over more than 40 years, this widespread tree disease has destroyed millions of UK elm trees and is still spreading north. 

Dutch elm disease is caused by a fungus but is spread by elm bark beetles. These introduce the spores into the tree’s water and nutrient transport system during feeding. As the fungus spreads and grows, the tree dies from nutrient deficiency.

Symptoms of Dutch elm disease include:

  • Dying of shoots from the top of the tree downwards
  • Leaves that turn yellow, wilt and drop off
  • ‘Shepherd’s crook’ shaped twigs
  • Dark spots under the bark of twigs
  • Dark patches or rings in twig cross-sections

Diseased elm trees should be felled as they can become a public safety hazard. When planting elm trees, hybrid plants should be considered as native elms will almost certainly become infected. Arborcure can help with both professional tree felling and commercial planting projects.

Ramorum tree disease

Ramorum disease is hard to detect but once established, can spread quickly.

The microscopic algae-like organism responsible is Phytophthora ramorum (the ‘plant destroyer’). It is similar to the disease responsible for the 19th Century Irish Potato Famine. 

Borne on wet, windy air currents, Ramorum disease is well-suited to the south west’s climate and poses a threat to a wide variety of native UK trees, particularly it’s main victim: larch trees. It first penetrates the tree’s leaves’ cell walls before spreading through its water and nutrient transport system.

Symptoms of Ramorum disease include:

  • Blackened areas where the leaves meet the stem and along the midribs
  • Black, wilted leaves/needles
  • Dieback of outermost branches

Since Ramorum disease can spread quickly and jump species (as it did to sweet chestnuts in a case in Devon in 2015), it is vital that suspected infections are dealt with quickly. We recommend contacting Arborcure for professional identification and felling.

Sweet chestnut blight

Another threat to the south west’s sweet chestnuts, Cryphonectria parasitica is a bright orange/yellow fungus which can take over the tree through fissures, wounds or grafting points. This tree disease was first found in the UK in 2011 and there were outbreaks in Devon in 2017.

Symptoms of sweet chestnut blight include:

  • Sunken cankers within cracks in the bark 
  • Brown, wilted leaves.
  • Evidence of stem girdling (where the cankers completely encircles a branch stem, cutting off nutrients)
  • Orange or yellow fruiting bodies on the bark
  • Long tendrils in humid conditions

Although this fungus is devastating to infected trees, it spreads slowly and in some cases carries a virus that prevents it from producing spores at all. Careful tree management from a company like Arborcure will help you contain an outbreak of this UK tree disease.

Acute oak decline

Although acute oak decline is not a specific UK tree disease, it is a big problem for our much-loved oak trees. Acute oak decline is not fully understood but appears to be a response to stress in the environment. This can come from extreme weather (droughts and floods), pollution and attacks from pests.

Symptoms of stressed oak trees include:

  • Sudden thinning of the crown
  • Dark, wet patches running down the bark
  • Intermittent stem bleeding

If you are responsible for oak trees displaying these systems you should not ignore it. Stressed oaks can become vulnerable to secondary tree diseases and can very quickly start to die.


If your trees are showing symptoms of any of the above UK tree diseases, please get in touch with Arborcure. We can provide an inspection and carry our any and all necessary felling and land management work.

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